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MUSCULAR  STRENGTH  AND  MUSCULAR  SYMMETRY  IN 

HUMAN  BEINGS  •  \ :. ;  ?  %  ; 

III.  IN  ADULT  MALES  ;"«  /t  •     ;;r'.c 

%„•/«*•,:..  ?ir  •• 
E.  G.  MARTIN  AND  W.  H.  RICH 

From  the  Laboratory  of  Physiology,  Leland  Stanford  Junior  University 

Received  for  publication  June  19,  1918 

Determinations  of  muscular  strength  in  human  beings  by  means  of 
dynamometers  have  been  made  in  large  numbers  by  numerous  investi- 
gators in  connection  with  various  problems  (1).  Among  the  problems 
so  approached  may  be  mentioned  studies  of  fatigue  (2)  and  of  rela- 
tionship between  physical  strength  and  intelligence  (3).  The  favorite 
instrument  in  these  studies  has  been  the  grip  dynamometer,  either  the 
old  form  of  Collin  or  the  improved  type  designed  by  Smedley  (1).  In 
spite  of  the  objections  that  have  been  urged  against  the  grip  dyna- 
mometer as  an  instrument  of  research,  much  valuable  information  has 
been  obtained  with  its  aid  (1).  It  presents,  however,  the  undoubted 
shortcoming  of  making  use  of  one  of  the  most  complex  musculatures  of 
the  body  and  a  musculature,  moreover,  which  receives  much  special 
training.  The  question  may  properly  be  raised  whether  the  strength 
of  the  grip  truly  represents  general  bodily  strength  or  whether  this  par- 
ticular musculature  may  not  reflect  special  conditions  to  an  exceptional 
degree.  A  test  of  strength,  to  be  quite  satisfactory,  should  afford  in- 
formation of  the  strength  of  the  body  as  a  whole.  Ideally  it  should 
include  all  the  important  muscle-groups;  practically  a  strength  test  is 
valid  if  proof  can  be  furnished  that  it  constitutes  a  fair  sample  of  the  entire 
strength. 

The  system  of  muscle-testing  in  course  of  presentation  in  the  series 
of  papers  of  which  this  is  the  second  (4)  differs  from  the  systems  previ- 
ously proposed  in  the  fundamental  fact  that  it  measures  "breaking 
strength"  of  muscles,  namely,  the  force  required  to  overcome  maximal 
resistance  rather  than  the  utmost  positive  effort,  as  in  other  methods. 
Which  system  is  better  can  be  determined  finally  only  by  continued 
experience  and  comparison.  Certain  advantageous  features  of  the 


783  fc9/ 


E.    G.    MARTIN    AND    W.    H.    RICH 


present  system  may  be  mentioned.  As  a  routine  feature  of  the  test 
the  subject  is  required  to  develop  resistance  at  the  command  "  hold 
hack"  uttered  sharply.  We  find  that  under  this  stimulus  the  maximum 
effort  is  elicited,  almost  as  a  reflex.  Only  by  deliberate  planning  on  the 


itage  dish 

«/•»»    fhf>  rii 


ution  of  strength  among  the  muscles,  adult  males.     For 
•ibution  for  children  of  13  to  18  years  is  given  also 


13    TO    18   YEARS 


Plantar  flexion. . 

Dorsal  flexion.  . . 

Inversion 

Inversion 

Thighs 

Adduction 

Abduction 

Extension 

Flex  on 

Knees 

Extension 

Flexion 

Shoulders 
Pectoralis 

Latissimus  dorsi 

Anterior  deltoid. 

Posterior  deltoid 
Forearms 

Extension 

-  Flexion 

Wrists 

Extension 

Flexion 

Fingers 

Extension 

Flexion 

Thumbs 

Adduction. . 


part  of  the  subject  will  less  than  his  best  effort  be  put  forth.  Thus  an 
element  of  reliability  is  introduced,  which  is  of  the  highest  importance. 
As  a  matter  of  fact  the  deliberate  attempt  to  make  an  inferior  showing 
is  instantly  revealed  in  the  changed  character  of  the  response.  Since 
the  spring  balance  with  which  the  strength  is  determined  is  held  in  the 


MUSCULAR    STRENGTH     AND     MUSCULAR     SYMMETRY     IN     MAN 


hands  of  the  operator,  the  line  of  pull  can  be  rectified  in  accordance  with 
the  position  of  the  subject.  The  maintenance  of  correct  lines  of  pull  is 
of  course  essential  to  the  validity  of  any  system  of  strength-testing. 
The  promptness  with  which  the  correct  position  can  bo  taken  is  a  feature 
of  this  method  which  becomes  valuable  as  a  saver  of  time  when  larj 
series  of  tests  are  being  carried  on. 

The  muscle-test,  The  system  of  muscle-testing  as  originally  developed 
is  described  elsewhere  (5).  The  list  of  muscles  included  in  the  complete 
test  is  set  down  in  table  1 .  For  the  series  of  tests  on  adults  on  which  this 
paper  is  based  certain  muscle-groups  were  regularly  omitted.  These 
were  a,  the  plantar  flexors,  which  are  so  strong  in  adults  as  to  make 
their  testing  a  matter  of  inconvenience,  since  a  lever  has  to  be  arranged 
for  multiplying  the  force  of  the  spring-balance  pull;  b,  the  finger  exten- 
sors, which  were  omitted  because  their  short  leverage  requires  the  sub- 
stitution of  a  special  narrow  sling  for  the  full-width  sling  used  with  the 
other  muscle-groups,  a  time  consuming  substitution,  and  in  this  par- 
ticular series  the  saving  of  time  was  an  important  consideration.  Tests 
of  finger  flexors  were  made  on  only  part  of  the  subjects.  Here  the 
short  leverage,  together  with  the  great  strength,  marks  the  group  as  less 
satisfactory  than  most  of  the  others.  Tests  of  the  wrist  flexors  were 
omitted  from  part  of  the  early  subjects  on  account  of  a  fear,  found 
later  to  be  unjustified,  that  testing  them  might  give  discomfort. 

Subjects.  The  adults  tested  were  students  or  instructors  in  this 
University.  For  assistance  in  obtaining  the  cooperation  of  these  indi- 
viduals we  are  indebted  to  the  Department  of  Military  Training  of 
Stanford  University,  for  whose  courtesy  we  wish  to  express  our  thanks. 
In  addition  to  the  fifty  adult  males  on  whom  the  report  is  primarily 
based,  we  had  access  to  the  records  of  an  equal  number  of  adult  females 
tested  by  Doctor  Mosher  and  one  of  us  (6).  There  were  also  available 
the  records  of  fifteen  adults  from  the  series  of  infantile  paralysis  cases 
reported  in  a  former  paper  (4),  and  more  than  a  hundred  "short" 
tests  (p.  34)  made  from  time  to  time  as  opportunity  offered.  In  many 
cases  duplicate  records  were  made  at  least  eight  hours  apart ;  about  one- 
fourth  of  the  subjects  were  tested  five  or  more  times. 

Object  of  the  experiments.  Our  object  in  these  experiments  was  in 
part  the  establishing  for  adults  of  the  constants  previously  worked  out 
for  children  (4).  In  addition  to  this,  however,  we  had  in  mind  the  pos- 
sibility that  this  system  of  testing  might  offer  certain  advantages  for 
the  routine  determination  of  strength  provided  it  could  be  shown  to  be 
scientifically  reliable  and  practical  in  application. 


E.    G.    MARTIN   AND   W.    H.    RICH 

The  complete  test,  as  outlined  in  table  1,  can  scare  '     ' 
through  m  )ess  th      a  half.hour  for 

abbreviate,  ,s  highly  desirable.     A  feasible  method  of  abbrevia 
would  be  to  make  actual  determinations  of  strength  of  a  few  mS 

TABLE  2 


strength,  56  adult, 


MUSCLE-GROUP 


COEFFICIENT  OF  CORRELATION 


Feet 

Plantar  flexion. 
Dorsal  flexion.. 

Inversion 

Eversion ; 

Thighs 

Adduction 

Abduction 

Extension 

Flexion 

Knees 

Extension 

Flexion 

Shoulders 

Pectoralis 

Latissimus  dorsi 
Anterior  deltoid. 
Posterior  deltoid 
forearms 

Extension 

Flexion 

Wrists 

Extension 

Flexion 

Fingers 

Extension 

Flexion 

Thumbs 

Adduction. . 


groups  only  and  to  compute  from  these  the  total  strength.     That  such 

a  method  ,s  valid  ,„  suggested  nra  former  paper  (Martin:  loe.  cit.,  p. 

task  here  ,s  to  verify  the  validity  of  this  idea  and  to  examine 

erent  muscle-groups  individually  to  see  which  should  be  inch,,!,,! 

m  the  abbreviated  test.     Since  the  first  criterion  of  an  abbreviated  test 


MUSCULAR    STRENGTH    AND    MUSCULAR    SYMMETRY    IN    MAN         3« 

must  be  its  reliability,  namely,  the  showing  that  it  represents  fairly  the 
total  strength,  the  muscles  selected  for  inclusion  should  be  those  that 
show  the  highest  correlation  of  individual  strength  with  the  total 
strength,  provided  the  muscles  are  found  to  differ  in  this  regard. 

For  comparing  the  strength  of  individual  muscles  with  the  total 
strength  of  the  body  we  used  a  series  of  fifty-six  cases  on  which  complete 
tests  (except  of  plantar  flexors  and  finger  extensors,  as  noted  above) 
had  been  made.  Records  of  wrist  flexion  and  of  finger  flexion  were 
missing  also  from  a  part  of  the  cases.  These  cases  were  tabulated  and 
the  Pearson  coefficient  of  correlation  of  each  muscle  with  the  total 
strength  calculated.  The  results  are  set  down  in  table  2.  Inspection 
of  this  table  shows  that  the  muscles  vary  among  themselves  in  the  extent 
to  which  their  individual  strength  [tends  to  bear  a  fixed  relation  to  the 
total  strength.  There  are  ten  pairs  in  which  the  correlation  of  each 
muscle  of  the  pair  with  the  total  strength  is  above  0.80,  with  a  probable 
error  of  not  to  exceed  ±0.032.  Evidently  a  short  test  will  be  most 
reliable  if  selected  from  among  these  ten  pairs  of  muscle-groups.  Inci- 
dentally it  may  be  noted  that  the  lowest  coefficients  of  correlation  in 
the  entire  series  were  given  by  the  finger  flexors,  which  are  the  muscle's 
used  in  tests  of  strength  with  grip  dynamometers.  It  is  probable  that 
these  coefficients  are  lower  than  would  be  given  by  tests  taken  with  per- 
fected instruments  of  the  Smedley  type,  but  the  fact  which  seems  to 
be  generally  true,  to  judge  from  table  2,  that  the  muscle-groups  with 
short  leverage  correlate  less  closely  than  do  those  with  long  leverage, 
indicates  that  the  original  selection  of  the  grip  as  a  criterion  of  bodily 
strength  was  perhaps  unfortunate. 

In  making  selection  for  a  short  test  from  among  the  ten  pairs  of 
muscle-groups  whose  correlations  with  total  strength  are  satisfactorily 
high,  the  determining  criterion  would  seem  to  be  altogether  that  of 
suitableness  for  the  practical  procedure  of  the  test.  The  application 
of  this  criterion  narrows  at  once  the  range  of  selection.  Thus  hip  ex- 
tensors, hip  flexors  and  knee  extensors,  although  correlating  well  with 
total  strength,  are  undesirable  from  the  practical  standpoint  because 
they  are  very  strong  muscles,  requiring  often  a  tension  of  two  hundred 
pounds  or  more  to  overcome  their  resistance,  and  the  great  labor 
involved  in  developing  this  high  tension  repeatedly  is  likely  to  prove 
too  exhausting  to  the  giver  of  the  tests.  The  knee  flexors  are  among  the 
most  satisfactory  muscles  tested  on  children,  but  with  adults  they  are 
likely  to  cramp  when  contracted  forcibly,  a  fact  which  constitutes  a 
valid  objection  to  their  use  in  a  routine  test.  There  remain  in  the 

inK    AMERICAN  JOURNAL    OF  PHYSIOLOGY,    VOL.    47.    NO.    1 


E.    G.    MARTIN   AND    W.    H.    RICH 


available  list  six  pairs  of  muscle-groups,  three  on  the  legs:  dorsiflexors 
of  the  foot,  adductors  of  the  thigh,  abductors  of  the  thigh;  and  three  on 
the  arms:  pectorals,  extensors  of  the  forearm,  flexors  of  the  forearm. 
Minor  considerations  suggest  the  elimination  from  the  short  test  of 
the  dorsiflexors  of  the  foot  and  the  extensors  of  the  forearm:  the  first 
because  removal  of  the  shoe  would  be  necessary,  the  second  because 
testing  of  the  forearm  extensors  involves  a  degree  of  care  in  placing  the 
parts  in  position  which  militates  against  speed  in  carrying  out  the  test. 
With  the  idea  that  the  test  might  be  found  available  in  industrial  stud- 
ies we  have  striven  to  reduce  the  time  required  to  the  least  possible 
figure.  The  four  pairs  of  muscle-groups  now  included  in  the  list  are  the 
adductors  and  abductors  of  the  thigh,  the  pectorals  and  the  flexors  of 
the  forearm.  Without  any  real  justification  but  merely  from  a  feeling 
that  the  muscles  which  move  the  hand  ought  to  have  representation  in 
the  short  test,  we  added  originally  to  this  list  the  flexors  of  the  wrist. 
Additional  experience  has  convinced  us,  however,  that  the  added  in- 
formation thus  obtained  is  not  of  sufficient  importance  to  justify  the 
additional  time  consumed  in  testing  the  wrist  muscles;  we  omit  them, 
therefore,  from  our  standard  short  test  as  here  proposed. 

'For  the  sake  of  completeness,  and  also  in  order  that  simple  direc- 
tions may  be  readily  available,  the  technique  of  the  short  test  is  here 
outlined. 

Apparatus  required.  An  ordinary  flat-face  spring-balance  with  a  scale  capac- 
ity of  200  pounds  by  2  pounds,  equipped  with  a  self-registering  index.  (There 
are  scales  on  the  market  with  self-registering  indices  but  these  are  heavier  than 
desirable.  We  have  found  it  satisfactory  to  fit  up  an  ordinary  scale  in  our  own 
shop  with  a  simple  device.)  A  stout  wood  handle  is  attached  by  a  swivel  to  the 
upper  end  of  the  scale,  and  a  loop  of  stout  leather  1J  inch  wide  and  30  inches  in 
circumference  is  attached  by  another  swivel  to  the  lower  end  of  the  balance. 

A  stout  table  65  feet  long  and  2£  feet  wide,  with  a  cleat  secured  firmly  across 
one  end.  A  cushion  on  which  the  subject's  head  may  rest  should  be  provided  with 
this  table,  * 

An  upright  post  4  inches  square  and  at  least  65  feet  high,  so  placed  that  it  is 
surrounded  on  at  least  three  sides  by  ample  space.  Some  form  of  hand-hold  is 
provided  by  which  the  subject  may  steady  himself  as  he  leans  against  the  post. 
(A  knotted  rope  tied  to  a  convenient  ring  near  by  answers  well  for  this  hand-hold.) 

Procedure:  General  instructions.  The  individual  to  be  tested  is  referred  to  as 
the  subject.  The  persons  giving  the  test  are:  first,  the  adjuster;  second,  the 
operator. 

The  duties  of  the  adjuster  are  to  place  the  loop  in  the  assigned  position  about 
the  arm  or  leg,  support  it  there  with  one  hand  and,  if  necessary,  the  arm  or  leg 
of  the  subject  with  the  other.  He  gives  the  command  "hold  back"  to  mark  the 
beginning  of  the  pull,  and  "stop"  to  mark  the  end. 


MUSCULAR    STRENGTH    AND     MUSCULAR    SYMMETRY     IN     MAN          «3O 

The  operator  has  the  handle  of  the  balance  in  his  right  hand  and  the  body 
of  the  balance  in  his  left. 

After  the  loop  is  adjusted  the  adjustor  gives  the  command  "hold  back."  At 
this  command  the  subject  contracts  with  all  his  power  the  muscle-group  being 
tested  and  simultaneously  the  operator  pulls  upon  the  spring-balance.  Tension 
must  be  developed  as  rapidly  as  possible  without  jerking,  and  must  be  increased 
until  the  resistance  of  the  subject  is  actually  overcome.  At  the  command  "stop" 
the  pull  is  discontinued  immediately.  The  scale  is  read  at  once  and  the  reading 
recorded  by  the  assisting  clerk.  The  sliding  indicator  of  the  scale  must  always 
be  returned  to  the  zero  position  immediately. 

Tests  are  taken  with  the  subject  fully  dressed. 

Muscle-groups  that  are  reported  by  the  subject  to  be  sore  are  not  tested. 

Calculation  of  total  strength.  The  sum  of  the  strengths  shown  by  the  individual 
muscles  included  in  the  short  test  constitutes  15  per  cent  of  the  entire  strength 
as  found  by  the  complete  test  (see  table  1).  To  calculate  the  entire  strength, 
therefore,  the  sum  of  these  determined  strengths  must  be  multiplied  by  the  re- 
ciprocal of  0.15,  which  is  6.67.  The  product  thus  obtained  is  the  figure  for  the 
strength  of  the  subject.  If  for  any  reason  any  muscle-group  was  omitted  from 
the  test,  assume  the  strength  of  the  omitted  muscle  to  be  the  same  as  that  of  the 
corresponding  muscle  on  the  other  side. 

Detailed  technique  of  the  tests,  a.  Pectorals.  The  subject  stands  at  attention 
with  the  middle  of  his  back  pressed  firmly  against  the  upright  post  and  the  hand 
of  the  arm  not  being  tested  grasping  the  hand-hold.  The  arm  to  be  tested  is 
allowed  to  be  limp  in  the  hands  of  the  adjustor  until  the  command  "hold  back," 
with  which  command  the  pectoral  muscles  are  contracted  as  strongly  as  possible. 
The  adjustor  stands  directly  in  front  of  the  subject,  facing  him;  places  the  loop  of 
the  balance  about  the  arm  to  be  tested,  just  above  the  elbow;  with  one  hand 
he  holds  the  loop  in  position  and  grasps  lightly  the  subject's  hand  or  wrist  with 
his  other  hand.  Keeping  the  subject's  arm  straight,  the  adjustor  draws  it  across 
the  subject's  body  as  far  as  possible,  keeping  it  as  close  to  the  body  as  can  be 
done  and  still  give  clearance  for  the  loop.  At  the  command  "hold  back"  the 
subject's  effort  is  to  hold  the  arm  from  being  drawn  backward  and  downward  from 
this  position.  The  operator,  standing  at  the  subject's  side,  holds  the  balance  in 
a  line  downward  and  backward  from  the  subject's  elbow  in  such  a  position  that 
the  arm  as  drawn  back  will  just  clear  the  subject's  body.  At  the  command  ' 'hold 
back"  the  operator  develops  sufficient  tension  to  draw  the  arm  down  to  the  side 
of  the  body.  The  command  "stop"  must  be  given  and  the  pulling  discontinued 
before  the  arm  has  been  drawn  beyond  the  vertical  line. 

b.  Forearm  flexors.  The  subject  lies  on  his  back  on  the  table  with  his  heels 
pressed  firmly  against  the  cleat,  The  adjustor  stands  at  the  subject's  left  for 
both  flexors.  His  right  hand  holds  the  subject's  elbow  to  the  table;  his  left  hand 
brings  the  subject's  forearm  into  a  position  of  flexion  about  15  degrees  toward  the 
shoulder  from  the  vertical,  and  adjusts  the  loop  about  the  wrist  so  that  its  upper 
edge  is  at  the  crease  in  the  skin  at  the  base  of  the  hand.  The  operator  stands  at 
the  foot  of  the  table ;  he  develops  tension  at  the  word  of  command.  The  command 
"stop"  should  be  given  when  the  forearm  reaches  the  vertical. 

c.   Thigh  adductors.     Position  of  the  subject  same  as  in  the  above  test  except 
that  he  presses  against  the  cleat  only  with  the  foot  of  the  leg  that  is  not  to  be 


3.    G.    MARTIN    AND    W.    H.    RICH 

tested.  He  may  steady  himself  by  grasping  the  edges  of  the  table.  The  adjuster 
stands  at  the  foot  of  the  table;  with  one  hand  he  places  the  loop  in  the  hollow 
just  above  the  malleolus  (an  equally  correct  index  is  to  have  the  loop  just  clear  of 
the  top  of  an  ordinary  man's  shoe);  he  seizes  the  subject's  heel  with  the  other 
hand;  lifts  the  leg  until  the  heel  is  just  high  enough  to  clear  the  other  toe,  and 
then  draws  the  leg  into  extreme  adduction.  The  toe  of  the  leg  to  be  tested  must 
be  kept  vertical.  The  operator  stands  at  the  side  of  the  table  and  develops  ten- 
sion at  the  word  of  command.  The  command  "stop"  should  be  given  as  soon  as 
the  leg  is  drawn  into  line  with  the  axis  of  the  body. 

d.  Thigh  abductors.  The  position  of  the  subject  and  of  the  adjuster  is  the 
same  as  in  the  above  test.  The  loop  is  placed  as  for  the  adductors  except  that 
the  direction  of  pull  is  opposite.  The  leg  to  be  tested  is  drawn  out  15  degrees  be- 
yond the  line  of  the  body;  the  effort  of  the  subject  at  the  command  "hold  back" 
is  to  prevent  the  operator  from  drawing  the  leg  into  line  with  the  body.  The 
command  "stop"  is  given  just  as  the  leg  reaches  tho  midline. 

The  most  convenient  order  for  the  tests  is  as  follows: 

Right  pectoral 
Left  pectoral 
Right  forearm  flexor 
Left  forearm  flexor 
Right  thigh  adductor 
Left  thigh  abductor 
Right  thigh  abductor 
Left  thigh  adductor 


Although  the  satisfactory  giving  of  the  test  requires  careful  training 
and  considerable  practice  on  the  part  of  operator  and  adjuster,  the 
demands  upon  the  subject  are  not  great.  We  have  made  successful 
tests  upon  subjects  with  a  very  limited  knowledge  of  English  and 
only  ordinary  intelligence.  Much  time  can  be  saved  by  letting  sub- 
jects not  yet  tested  see  the  test  carried  out  on  others.  In  this  way  they 
learn  what  is  expected  of  them  and  carry  out  their  part  promptly 
when  their  turn  comes.  A  few  seconds  over  one  minute  is  usually 
enough  time  for  carrying  out  a  short  test. 

Certain  relationships  which  can  readily  be  carried  in  mind  are  help- 
ful in  connection  with  the  making  of  tests,  especially  where  there  is 
suspicion  of  malingering.  Thus,  as  table  1  shows,  pectorals  and  fore- 
arm flexors  are  of  nearly  equal  strength,  as  are  thigh  adductors  and  ab- 
ductors, and  the  former  groups  are  slightly  less  than  twice  as  strong  as 
the  latter.  In  men  of  ordinary  strength  pectoral  and  forearm  flexors 
are  likely  to  range  between  75  and  100  pounds,  and  thigh  adductors 
and  abductors  between  40  and  60  pounds.  Of  fifty-five  adult  males 
selected  at  random,  80  per  cent  of  the  muscles  of  the  short  test  fell 
within  these  limits. 


MUSCULAR    STRENGTH     AND     MUSCULAR    SYMMETRY    IN    MAN 

That  the  proposed  short  test  is  practicable  we  believe  these  observa- 
tions demonstrate.  That  it  gives  a  reliable  picture  of  the  entire  strength 
can  reasonably  be  assumed  from  the  fact  that  each  individual  muscle- 
group  included  in  the  test  correlates  well  with  the  entire  strength.  One 
would  expect  to  find  that  the  summed  strength  of  these  several  muscle- 
groups  would  correlate  with  the  entire  strength  even  better  than  do 
the  individual  muscle-groups.  That  this  is  the  case  was  shown  by  a 
comparison,  on  the  same  series  of  adults  on  which  the  correlation  of 
individual  muscles  were  worked  out,  of  the  summed  strength  of  the 
muscles  of  the  short  test  with  the  entire  strength.  The  coefficient  of 
correlation  of  this  comparison  was  0.94  ±  0.01.  So  high  a  correlation 
constitutes  sufficient  demonstration  that  the  short  test  is  a  reliable 
indicator  of  the  entire  strength. 

Although  the  expression  "entire  strength"  as  here  used  applies  actu- 
ally only  to  that  part  of  the  strength  represented  by  the  muscle-groups 
of  the  complete  test  as  outlined  in  table  1,  these  observations  show  that 
in  all  probability  the  real  "entire  strength"  bears  a  fixed  relationship  to 
the  strength  of  the  muscles  included  in  the  complete  test  and  also,  there- 
fore, to  the  short  test.  The  principle  of  "random  sampling"  applies 
here.  The  muscle-groups  included  in  the  complete  test  constitute  a 
fairly  large  sample  of  the  whole  musculature.  Individual  muscles 
and  small  groups  of  muscles  correlate  well  with  the  summed  strength, 
of  the  complete-test  (see  above,  also  Martin:  loc.  cit.,  p.  72).  There 
is  no  physiological  or  statistical  principle  that  would  justify  any  other 
assumption  than  that  the  muscle-groups  not  included  in  the  complete 
test  correlate  equally  well  with  it  and  with  each  other. 

Muscular  symmetry.  In  the  first  paper  of  this  series  (4)  the  distri- 
bution of  strength  among  the  muscles  of  the  body  in  children  was 
shown  to  vary  somewhat  with  age  so  that  three  distinct  age-groups 
could  be  established  (loc.  cit.,  p.<  71).  The  symmetry  of  individuals  was 
shown  to  deviate  from  the  ideals  as  set  down  in  the  table  by  varying 
amounts,  averaging  for  the  entire  series  Hi. 7  per  cent  (loc.. cit.,  p. 
table).  Application  of  the  method  there  described  to  the  present 
series  of  adult  males  gives  the  figures  for  percentage  strength  distribu- 
tion that  are  presented  in  table  1  of  this  paper.  These  figures  are  aver- 
ages of  sufficient  data  except  for  plantar  flexion  and  finger  extension; 
the  observations  on  which  those  values  were  obtained  are  fewer  than 
desirable.  Considerable  errors  in  these  two  values  would  a  fleet  the 
others  of  the  series  only  slightly,  however,  and  it  is  felt  that  they  are 
sufficiently  close  approximations  for  present  purposes. 


E.    G.    MARTIN    AND   W.    H.    RICH 


The  deviations  of  individuals  from  ideal  symmetry  are  decidedly  less 
in  this  series  of  adult  males  than  in  the  series  of  children  presented  in 
the  former  paper.  The  average  mean  deviation  for  this  series  is  10.7 
as  compared  with  16.7  for  the  former.  In  fact,  the  greatest  deviation 
in  this  series,  a  deviation  of  16.5,  is  less  than  the  average  for  children. 
We  were  quite  unprepared  to  find  adults  more  symmetrical  as  a  class 
than  children  and  are  inclined  to  think  that  we  may  have  happened  upon 
an  exceptionally  symmetrical  group.  Most  of  them  were  college  un- 
dergraduates and  engaged  at  the  time  when  these  tests  were  being 
made  in  intensive  military  training. 

The  relation  of  strength  to  weight.  A  point  on  which  stress  was  laid  in. 
the  former  paper  (4)  was  that  the  ratio  of  strength  to  weight  in  chil- 
dren tends  to  be  constant.  That  the  same  would  hold  for  adults  seems 
unlikely,  chiefly  because  so  many  other  factors  in  addition  to  weight  be- 
come operative  in  adults  in  determining  strength.  In  the  former 
paper  (p.  74)  mention  was  made  of  the  fact  that  boys  of  seventeen  and 
eighteen  years  show  higher  strength-weight  ratios  than  do  younger 
boys,  showing  the  beginnings  of  departure  from  the  childish  condition 
and  suggesting  the  incidence  of  additional  factors. 

For  a  study  of  the  relation  of  strength  to  weight  we  had  available 
a  series  of  one  hundred  and  twenty-two  adult  males.  This  included 
our  Stanford  instructors  and  students,  a  few  cases  from  the  infantile 
paralysis  series  mentioned  above,  and  a  number  of  recent  army  recruits 
that  we  were  enabled  to  test  through  the  courtesy  and  cooperation  of 
various  army  officers.  The  group  as  a  whole  would  be  considered  as 
made  up  of  outdoor  men.  The  Stanford  students,  as  previously  noted, 
were  most  of  them  taking  intensive  military  training.  The  weights 
ranged  from  107  to  196  pounds,  averaging  146.6.  The  strengths  ranged 
from  2000  to  5800  pounds,  averaging,  in  round  numbers,  3900.  (A 
single  individual,  the  college  strong  man,  weighing  208  pounds,  made  a 
strength  record  of  7600  pounds.  This  is  so  far  in  excess  of  our  other 
records  that  we  do  not  include  it  among  our  averages).  The  ratios  of 
strength  to  weight  ranged  from  19  to  37,  averaging  26.6.  We  are  in- 
clined to  think  that  our  figures  for  average  strength  and  average  strength- 
weight  ratio  are  somewhat  higher  than  they  would  be  for  adult  males 
in  general. 

As  would  be  expected,  there  is  a  moderate  correlation  between  strength 
and  weight,  the  coefficient  for  this  series  being  0.58  =*=  0.04.  This  ac- 
cords with  the  familiar  fact  that  on  the  whole  large  men  are  stronger 
than  small  men.  The  correlation  is  not  close  enough,  however,  to 


MUSCULAR     STRENGTH    AND     MUSCULAR     SYMMETRY     IN    MAN 


indicate  that  with  adults,  as  with  children,  the  body-weight  is  the  domi- 
nant factor  in  determining  strength.  Whipple  (loc.  cit.,  p.  114)  cites 
observations  of  correlation  between  strength  and  weight,  in  which 
strength  was  tested  by  a  different  method,  with  the  following  results: 
at  Oxford,  coefficient  of  correlation  0.46;  at  Cambridge,  coefficient  of 
correlation  0.56. 

The  significance  of  the  strength-weight  ratio.  Where  two  individuals 
of  equal  weight  differ  widely  in  strength  there  are  evidently  at  least 
four  factors  which  may  have  influence  in  accounting  for  the  difference. 
The  first  of  these  is  actual  amount  of  muscular  tissue.  There  are  un- 
doubtedly considerable  variations  in  the  amounts  of  muscle  substance 
present  in  the  bodies  of  persons  whose  total  weight  is  the  same.  A  sec- 
ond factor  is  bodily  configuration.  It  is  quite  conceivable  that  cer- 
tain configurations  lend  themselves  more  favorably  to  effective  exhi- 
bitions of  muscular  power  than  do  others.  Information  on  this  point 
is  lacking  although  it  should  be  stated  that  in  respect  to  t lie  factor  of 
height  as  an  element  in  bodily  configuration  we  have  not  been  able  to 
secure  any  evidence  that  it  has  significance.  In  investigating  this 
point  we  grouped  all  our  cases  according  to  weight,  using  group  inter- 
vals of  five  pounds,  and  then  arranged  all  the  members  of  each  group  in 
ascending  order  of  height.  We  then  examined  the  distribution  of  the 
strongest  and  next  strongest  members  of  each  group  with  relation  to 
height,  and  similarly  of  the  weakest  and  next  weakest.  We  found, 
however,  nothing  significant.  One-half  the  strong  were  among  the 
short  men  and  the  other  half  among  the  tall.  Substantially  the  same 
distribution  appeared  also  among  the  weak.  Furthermore,  the  average 
strengths  of  the  short  and  tall  halves  of  each  group  were  virtually  equal. 

A  third  factor  is  muscle-quality,  and  this  undoubtedly  has  much  to  do 
with  determining  the  strength.  The  fourth  factor  we  may  call,  for 
lack  of  a  better  term,  innervation.  There  can  be  little  doubt  that  indi- 
viduals vary  in  the  extent  to  which  they  are  able,  by  volition,  to  elicit 
muscular  effort.  That  the  usual  manifestations  fall  far  short  of  the 
potential  maximum  is  shown  by  the  familiar  effects  of  excitement,  as 
in  the  "strength  of  desperation."  We  have  been  at  pains  in  the  de- 
velopment of  our  procedure  to  avoid  introducing  the  factor  of  excite- 
ment. The  attempt  has  been  to  base  the  showing  upon  a  maximal 
volitional  effort  made  rather  as  a  matter  of  routine  than  as  a  feature  of 
competition  or  of  desire  to  establish  a  record.  Our  feeling  has  been 
that  a  maximum  effort  made  in  "cold  blood"  gives  a  more  uniform,  and 
probably  also  a  truer  picture  of  the  neuro-muscular  power  than  would 


*:.    G.    MARTIN   AND    W.    H.    RICH 

a  similar  effort  made  under  the  stimulus  of  excitement.  On  the  whole, 
muscle  quality  and  innervation  seem  to  us  the  factors  most  likely  to 
dominate  in  the  determination  of  strength,  and  in  accordance  with  this 
view  we  are  inclined  to  interpret  high  strength-weight  ratios  as  indi- 
cative of  good  muscle-quality  and  good  innervation  and  low  strength- 
weight  rat os  as  indicative  of  poor  muscle-quality  and  poor  innervation. 
Further  investigation  will  be  necessary  before  these  factors  can  be 
separated ;  indeed  it  is  quite  within  the  bounds  of  physiological  possibility 
that  they  are  not  separable;  that  excellence  in  one  feature  is  always  bound 
up  with  excellence  in  the  other  and  vice  versa. 

Physical  classification.  For  convenience  in  assigning  individuals  to 
categories  in  accordance  with  their  physical  strength,  some  simple 
scheme  of  classification  is  desirable.  If  our  assumption  is  correct  that 
the  strength-weight  ratio  is  an  index  of  muscle-quality  and  of  inner- 
vation it  would  suggest  itself  as  a  sound  basis  on  which  to  work  out 
such  a  classification.  The  limits  of  any  such  classification  must  be 
more  or  less  arbitrary,  at  least  until  sufficient  data  are  accumulated  to 
enable  them  to  be  established  by  reference  to  a  normal  probability 
curve.  If  we  are  correct  in  our  assumption  that  the  averages  of  our 
present  series  are  somewhat  higher  than  would  hold  for  adult  males  in 
general,  the  distribution  of  our  cases  about  their  average  is  not  strictly 
comparable  with  the  true  distribution  for  adult  males.  We  feel  dis- 
posed, therefore,  to  suggest  tentatively  somewhat  lower  limits  for  our 
proposed  classes  than  would  be  indicated  by  our  data  taken  by  them- 
plves.  The  limits  of  the  proposed  classes  are  given  in  the  subjoined 


more  than  30 

„ 25.1-30 

C 20.1-25 

D 16.1-20 

J less  than  16.1 

The  distribution  of  individuals  in  our  series  of  122  is  as  follows: 
class  A,  17  (14  per  cent);  class  B,  56  (46  per  cent);  class  C,  47  (38  per 
cent) ;  class  D,  2  (2  per  cent) ;  class  E,  none.  In  general  terms  we  would 
say  that  class  A  includes  exceptionally  strong  men;  class  B,men  of  more 
than  average  strength;  class  C,  men  of  average  strength;  class  D,  men 
of  less  than  average  strength ;  and  class  E,  decided  weaklings.  Although 
our  series  included,  according  to  this  classification,  no  E  men  and  only 
two  D  men,  we  think  it  altogether  likely  that  a  more  representative 


MUSCULAR     STRENGTH    AND     MUSCULAR     SYMMETRY     IN    MAN 

series,  one  in  which  clerks  and  factory  hands  were  represented,  would 
contain  a  due  proportion  of  D  men  and  a  reduced  percentage  of  A  and 
B  men.  We  are  doubtful  whether  many  healthy  adult  males  will  be 
encountered  whose  strength  is  so  slight  as  to  put  them  into  the  E  class 
although  our  experience  among  the  classes  of  the  population  in  which 
marked  physical  weakness  is  likely  to  prevail  is  practically  nil. 

This  classification,  based  on  the  strength-weight  ratio,  draws  no* 
distinction  between  small  men  of  good  quality  and  large  men  of  equally 
good  quality,  although  the  latter  will  obviously  be  actually  much  more 
powerful  than  the  former.  For  the  practical  purpose  of  assigning  men 
to  categories  in  accordance  with  their  ability  to  achieve  it  would  ap- 
pear that  some  modification  of  the  classification  might  well  be  made  in 
which  there  is  recognition  of  the  importance  of  absolute  muscular  power 
as  well  as  of  good  muscle-quality  and  good  innervation.  This  end 
would  be  achieved  if  definite  lower  limits  of  strength  were  assigned 
to  each  class.  Tentatively  we  would  suggest  the  following  limits: 
class  A,  5000  pounds;  class  B,  4000  pounds;  class  C,  3000  pounds;  class 
D,  1600  pounds.  The  practical  effect  of  these  absolute  limits  would 
be  to  require  small  men  to  show  higher  strength-weight  ratios  than  large 
men,  if  they  are  to  be  placed  in  the  higher  classes.  In  no  case  would  we 
reduce  the  limits  suggested  for  the  strength-weight  ratios  of  the  differ- 
ent classes.  It  would  follow  that  a  man  weighing  distinctly  more  than 
the  average  would  have  to  show  a  strength  well  above  the  lower  abso- 
lute limit  of  any  given  class  in  order  to  attain  a  strength-weight  ratio 
that  would  admit  him  to  it . 


1.  The  distribution  of  strength  among  the  muscles  m  a<n 
given  (table  1). 

2.  The  correlation  between  the  strength  of  individual  muscles  and 
the  entire  strength  is  given  (table  2). 

3.  Statistical  evidence  is  presented  showing  that  estimations  of  entire 
strength  based  on  actual  determinations  of  the  strength  of  a  few  muscle- 
groups  are  valid. 

4.  Four   pairs   of   muscle-groups:  pectorals,    forearm    flexors,    thigh 
adductors  and  thigh  abductors  are  shown  to  correlate  individually  with 
entire  strength  to  a  satisfactory  degree  and  to  be  also  practically  adapted 
for  testing.     They  are  selected,  therefore,  as  constituting  the  "short" 


5.  The  technique  of  the  short  test  is  presented  in  de 


E.    G.    MARTIN   AND    W.    II.    RICH 

6.  The  summed  strength  of  the  muscles  of  the  short  test  is  shown 
)  correlate  well  with  the  entire  strength,  the  coefficient  being  0.94 

ie  adult  males  of  this  series  are  shown  to  have  a  highe 
symmetry  than  the  children  of  the  former  series;  the  averak.  «  ,u  < 
as  compared  with  16.7. 

8.  The  ratio  of  strength  to  weight  does  not  show  the  tendency  to  be 
constant  in  adult  males  that  is  seen  in  children.     There  is,  however,  a 
moderate  correlation  between  strength  and  weight. 

9.  The  factors  influencing  the  strength-weij 

The  conclusion  is  drawn  that  a  high  ratio  signifies  good  rnuscle-quamy 
and  good  innervation. 

10.  A  physical  classification,  based  primarily  on  the  strength-weight 
ratio  but  modified  to  take  some  account  of  actual  strength,  is  proposed. 

BIBLIOGRAPHY 

(1)  For  the  important  early  references  and  a  description  of  various  types  of 

dynamometers  see  WHIFFLE:  Manual  of  mental  and  physical  tests 
2nd  ed.,  i,  Baltimore,  1914. 

(2)  SCHUYTEN:  Arch.  d.  psychol.,  1903,  ii. 

(3)  SMEDLEY:  46th  An.  Kept,  Chicago  Bd.  of  Educ.,  1899. 

(4)  MARTIN:  This  Journal,  1918,  xlvi,  67. 

(5)  LOVETT  AND  MARTIN:  Amer.  Journ.  Orthop.  Surg.,  1916,  xiv,  415. 

(6)  MOSHER  AND  MARTIN:  Journ.  Amer.  Med.  Assoc.,  1918,  Ixx  140. 


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